Business, science and entertainment, applications depend upon computers to process and record data, often with large volumes of the data being stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical means of storing or archiving the data. Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is now measured in hundreds of gigabytes on 512 or more data tracks.
The improvement in magnetic medium data storage capacity arises in large part from improvements in the magnetic head assembly used for reading and writing data on the magnetic storage medium. A major improvement in transducer technology arrived with the magnetoresistive (MR) sensor originally developed by the IBM® Corporation. Later sensors using the GMR effect were developed. AMR and GMR sensors transduce magnetic field changes to resistance changes, which are processed to provide digital signals. Data storage density can be increased because AMR and GMR sensors offer signal levels higher than those available from conventional inductive read heads for a given read sensor width and so enable smaller reader widths and thus more tracks per inch. Moreover, the sensor output signal depends only on the instantaneous magnetic field intensity in the storage medium and is independent of the magnetic field time-rate-of-change arising from relative sensor/medium velocity. In operation the magnetic storage medium, such as tape or a magnetic disk surface, is passed over the magnetic read/write (R/W) head assembly for reading data therefrom and writing data thereto.
FIG. 1 illustrates a traditional flat-lapped bi-directional, two-module magnetic tape head 100, in accordance with the prior art. As shown, the head includes a pair of bases 102, each equipped with a module 104. The bases are typically “U-beams” that are adhesively coupled together. Each module 104 includes a substrate 104A and a closure 104B with readers and writers 106 situated therebetween. In use, a tape 108 is moved over the modules 104 along a tape bearing surface 109 in the manner shown for reading and writing data on the tape 108 using the readers and writers 106. Conventionally, a partial vacuum is formed between the tape 108 and the tape bearing surface 109 for maintaining the tape 108 in close proximity with the readers and writers 106.
Two common parameters are associated with heads of such design. One parameter includes the tape wrap angles αi, αo defined between the tape 108 and a plane 111 in which the upper surface of the tape bearing surface 109 resides. It should be noted that the tape wrap angles αi,αo includes an inner wrap angle αi which is often similar in degree to an external, or outer, wrap angle αo. The tape bearing surfaces 109 of the modules 104 are set at a predetermined angle from each other such that the desired inner wrap angle αi is achieved at the facing edges. Moreover, a tape bearing surface length 112 is defined as the distance (in the direction of tape travel) between edges of the tape bearing surface 109. The wrap angles αi, αo and tape bearing surface length 112 are often adjusted to deal with various operational aspects of heads such as that of FIG. 1, in a manner that will soon become apparent.
During use of the head of FIG. 1, various effects traditionally occur. FIG. 2A illustrates a first known effect associated with the use of the head 100 of FIG. 1. When the tape 108 moves across the head as shown, air is skived from below the tape 108 by a skiving edge 204 of the substrate 104A, and instead of the tape 108 lifting from the tape bearing surface 109 of the module (as intuitively it should), the reduced air pressure in the area between the tape 108 and the tape bearing surface 109 allows atmospheric pressure to urge the tape towards the tape bearing surface 109.
Regarding additional effects, it has also often been observed that the tape tends to exhibit tape lifting 205, or curling, along the side edge of the tape bearing surface 109 as a result of air leaking in at the edges and tape mechanical effects. This effect is shown in FIG. 2B. Particularly, the edges of the tape curl away from the tape bearing surface 109, resulting in edge loss or increased spacing between the edges of the tape and the tape bearing surface 109 as well as results in additional stress at points 206 which, in turn, may cause additional wear. Further augmenting such tape lifting 205 is the fact that many types of tape 108 naturally have upturned edges due to widespread use of technology applied in the video tape arts.
Allowing the media to contact the head often provides the best possible signal, as the effects of spacing loss are at a minimum. However, one problem with media-head contact is that of wear, particularly near the elements 106. FIG. 2C illustrates the head 100 of FIG. 1 prior to significant tape-induced wear. As shown in the detail, the readers and writers 106 are formed above the substrate 104A. An overcoat 150 is typically formed above the readers and writers 106 during fabrication.
FIG. 2D illustrates the same head 100 after wear has occurred. As shown in FIG. 2D, the overcoat 150, typically formed of alumina, tends to erode more rapidly than other portions of the head in contact with the moving tape. As the overcoat recedes, materials forming and surrounding the readers and writers 106 tend to wear more rapidly due to loss of overcoat support, as shown in FIG. 2E.
The resultant recession is detrimental because the magnetic medium does not conform well to the recessed region, thus resulting in spacing loss. The spacing loss is such that high frequencies are attenuated more than low frequencies. As is well, known, high frequency loss due to increased magnetic spacing between tape and recording elements tends to degrade drive performance, which is characterized by an increase in read errors.
The only known solutions for controlling erosion are to use low deposition rate aluminum oxide for the overcoat, which adds significantly to processing time; or to reduce the substrate-closure spacing, but write coil design requirements force a relatively large lower bound in this approach.